Legislation to ban applications of phosphorus on turf seems to be spreading across the country like a pandemic. Good idea? Probably not. For whatever reason, politicians like logical extremes, which invariably lead to illogical legislation.
Phosphorus (P) runoff into waterways causes eutrophication, i.e., the process in which water is enriched with dissolved nutrients, stimulating aquatic plants to grow and deplete dissolved oxygen. The problem is real and concerns are valid, but the source of P runoff is not from turf fertilizer and there’s plenty of peer-reviewed research supporting this contention.
In one such study, a comparison between the amount of P contained in surface runoff from fertilized turf and unfertilized prairie grass shows no significant difference over the course of the study (Steinke, K. et al., 2007). In fact, researchers found that during the seasons when the ground was not frozen, run-off from fertilized turf was significantly lower than the unfertilized prairie.
In another study, scientists found that just 15 meters of turf interrupting surface runoff filtered 89 percent of its sediments (Abu-Zreig, M., et al., 2003). Another study (Patty, L., et al. 1997) duplicated Abu-Zreig’s results and made the following observation:
“Vegetation within the flowpath increases water infiltration and decreases water turbulence, thus enhancing pollutant removal by sedimentation within filter media and infiltration through the filter surface.”
In yet another study, more dissolved P was discovered in leaf surface runoff from living plants than from the soil whether applications of P fertilizer were made or not (Sharpley, A.N. 1981).
Dr. Wayne R. Kussow, professor emeritus from the University of Wisconsin, researched phosphorus losses from lawns for six years and has recently completed a book (soon to be published by the American Chemical Society). In it he writes:
“Regulatory agencies need to be made aware that fertilizer and soil are not the only sources of P in lawn runoff water. A prominent source is vegetation in the landscape. How prominent remains to be conclusively demonstrated by further research. Laboratory measurements of P leached with water from grass clippings taken from research plots in this study indicated that the grass itself could potentially have been the sole source of P in both summer and winter runoff water. The obvious implication is that as long as lawns remain a prominent feature in urban landscapes, much of the P in runoff water is not amenable to regulation.”
He also writes:
“This study failed to provide evidence that not applying fertilizer P when soil test P was excessive will significantly reduce runoff P losses when no sediment loss occurs. Furthermore, the data of Barten and Jahnke show that even when sediment losses occur, runoff water total and soluble reactive P concentrations bear no significant relationships to soil test P levels. Therefore, use of soil test P as criteria for regulating fertilizer P application is inappropriate.”
This observation is not an endorsement of indiscriminate applications of phosphatic fertilizer, but points out that the relationship between soil P and runoff P are not necessarily linked.
There are also climatic factors that may contribute to eutrophication, such as higher temperatures and more precipitation. Clearly, greater amounts of rain (and snow) increase the likelihood of surface runoff from both plants and soil, and higher temperatures exacerbate the problem by stimulating and accelerating aquatic plant growth.
Overall, contemporary research strongly suggests that:
1. The vast majority of P entering open bodies of water is from surface runoff (especially when the ground is frozen);
2. Dissolved and particulate forms of P are extracted from many sources other than fertilizer; and
3. Dense vegetation, such as turf, has proven to be the best natural filter for trapping runaway nutrients.
And, without adequate P, turf quality—i.e., the quality of our filter—may decline. So, why are politicians jumping on this ban wagon? Good question and not easily answered. It could be the political hierarchy of agriculture verses turf. Since surface runoff over unvegetated ground clearly carries more sediment, regularly tilled fields—fertilized or not—lose more nutrients. Though effort to mitigate this obvious nonpoint source pollution is apparent, politically sacrosanct agriculture has customarily been held in much higher esteem than turf, and if politicians want to appear as though they are addressing the issue, it could be that turf is an acceptable scapegoat.
On the surface—and likely, right through to the core—it appears that legislation to ban applications of phosphorus on turf will, at the very least, accomplish nothing, but might make matters worse. And, intentional or not, the ban will effectively discriminate against organic fertilizers, the ingredients of which are residues from organisms that all required phosphorus to live.
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